**Core Concept**
Hypocalcemia, a condition characterized by low calcium levels in the blood, is a known complication post-thyroidectomy due to accidental injury to the parathyroid glands during surgery. This leads to a decrease in the production of parathyroid hormone (PTH), which is essential for maintaining normal calcium levels.

**Why the Correct Answer is Right**
The patient's symptoms of muscle cramps, Chvostek's sign (twitching of the facial muscles in response to tapping the facial nerve), and Trousseau's sign (carpal spasm in response to inflating a blood pressure cuff) are indicative of hypocalcemia. Chvostek's and Trousseau's signs are clinical manifestations of hypocalcemia, which occurs when there is an imbalance between the absorption and excretion of calcium, leading to a decrease in ionized calcium levels. In this case, the patient's parathyroid glands were likely damaged during surgery, resulting in decreased PTH production and subsequent hypocalcemia.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not directly relate to the patient's symptoms and postoperative thyroidectomy.
* **Option B:** This option is incorrect because it is unrelated to the clinical presentation and does not address the underlying cause of hypocalcemia.
* **Option D:** This option is incorrect because it is a treatment for hypocalcemia, not a cause or a symptom.

**Clinical Pearl / High-Yield Fact**
It is essential to monitor calcium levels post-thyroidectomy, as hypocalcemia can occur due to accidental injury to the parathyroid glands during surgery. Early recognition and treatment of hypocalcemia are crucial to prevent complications such as muscle cramps, tetany, and seizures.

**Correct Answer:** C. Hypocalcemia secondary to accidental injury to the parathyroid glands during thyroidectomy.